High crimp, high strength rayon filaments and staple fibers

ABSTRACT

High tenacity rayon filaments and staple fibers having an exceptionally high number of crimps per inch are produced by spinning a viscose spinning solution into a coagulating-type spin bath to obtain coagulated, incompletely regenerated viscose filaments, the coagulated viscose filaments withdrawn from the spin bath being stretched from about 120 to 280 percent in length while the filaments are still substantially soluble in dilute alkali solution, the filaments being treated with a hot acid bath while being stretched. The tension of the filaments is then relaxed about 20-60 percent while the filaments are less than 50 percent regenerated, and the thus relaxed partially regenerated filaments are treated with an alkaline solution having a pH of from about 7.5 to 10. Regeneration of the filaments, or of staple fibers prepared therefrom, is then completed without additional stretching, followed by conventional desulfurization and washing of the highly crimpled filament or staple fiber product.

[11 3,793,136 451 Feb. 19, 1974 HIGH CRIMP, HIGH STRENGTH RAYON FILAMENTS AND STAPLE FIBERS Inventors: George C. Daul, Whippany; Fabian P. Burch, Succasunna, both of NJ.

Assignee: Rayonier Incorporated, New York,

[22] Filed: July 16, 1971 [21] Appl. No.: 163,485

Related U.S. Application Data [62] Division of Ser. No. 719,919, April 9, 1968, Pat. No.

[52] US. Cl. 161/173, 161/172, 264/168, 264/188, 264/196, 264/197 [51] Int. Cl. D02g 1/00, DOlf 3/28, DOld 5/22 [58] Field of Search.... 161/173, 172; 264/188, 196,

[56] References Cited I UNITED STATES PATENTS 3,689,622 9/1972 Kawai et al. 264/197 3,697,637 10/1972 Kawai et al..... 264/168 3,720,743 3/1973 Stevens et al 264/168 2,238,977 4/1941 Jackson et al. 161/173 2,942,931 6/1960 Mitchell et al 264/193 3,494,996 2/1970 Stevens et al 264/197 3,632,468 l/l972 Daul et al.' 161/173 Primary Examiner--Alfred L. Leavitt Assistant Examiner-Robert A. Dawson Attorney, Agent, or FirmJames B. Raden; Harold J.

Holt

[5 7 ABSTRACT High tenacity rayon filaments and staple fibers having an exceptionally high number of crimps per inch are produced by spinning a viscose spinning solution into a coagulating-type spin bath to obtain coagulated, incompletely regenerated viscose filaments, the coagu lated viscose filaments withdrawn from the spin bath being stretched from about 120 to 280 percent in length while the filaments are still substantially soluble in dilute alkali solution, the filaments being treated with a hot acid bath while being stretched. The tension of the filaments is then relaxed about 20-60 percent while the filaments are less than 50 percent regenerated, and the thusrelaxed partially regenerated filaments are treated with an alkaline solution having a pH of from about 7.5 to 10. Regeneration of the filaments, or of staple fibers prepared therefrom, is then completed without additional stretching, followed by conventional desulfurization and washing of the highly crimpled filament or staple fiber product.

1 Claim, 2 Drawing Figures mim cs FILAMENT C OAGULATION STRETCHING HOT, DILUTE (PARTIAL R ACID TREATMENT EGENERATIONI RELAXED ALKALINE TREATMENT (DILUTE NuOH,NuHCO ,Nu CO ,etc.I

ACID TREATMENT, REGENERATION (CUTTING INTO STAPLE FIBER OPTIONAL AT THIS POINT) PAIENIEIJ 3. 793. 136

SHEET 1 III 2 VISCOSE SPINNING FILAMENT COAGULATION FIG. I

I. STRETGHING HOT,DILUTE ACID TREATMENT (PARTIAL REGENERATION) ACID TREATMENT, REGENERATION (CUTTING INTO STAPLE FIBER OPTIONAL AT THIS POINT) FINISHING (DESULFURING, NEUTRALIZING,WASHING, FINISH APPLICATION) PATENIEB FEB I 9 I974 SHEET 2 (IF 2 AZOCbDQOmm mum; wJmaFm mom W n N .2: :1 mm m 295 533 5525:: 12m zEm HIGH CRIMP, HIGH STRENGTH RAYON FILAMENTS AND STAPLE FIBERS This is a division of application Ser. No. 719,919, filed Apr. 9, 1968 and now US. Pat. No. 3,632,468.

BACKGROUND OF THE INVENTION The US. Pat. No. 3,494,996 of H. D. Stevens, R. B. Kennedy, and G. C. Daul, describes a process for producing rayon fiber having a high wet modulus and high conditioned and wet tenacity. In this prior process a modified viscose spinning solution prepared, for example, by the procedure described in US. Pat. No. 2,942,931 is spun at a temperature of from 18-30 C. into a coagulating type spin bath. The coagulated partially regenerated filaments withdrawn from the spin bath are stretched, and completely regenerated, in accordance with the procedure described in the application. The rayon filaments and staple fibers produced by the foregoing process have an average conditioned tenacity of about 6 grams per denier (gpd), a wet tenacity within the range of from 3 to 5 gpd, and a wet modulus (wet tenacity at 5 percent elongation) of about 1 to 2 gpd. The fibers'have fewer than crimps or undulations per inch and, therefore, can be regarded as an essentially uncrimped fiber product.

In the course of subsequent experimental work in connection with the foregoing process, we have made the surprising discovery that a bulky, wool-like rayon filament or staple fiber product can be produced by making certain critical changes in the final stages of the spinning step of the process. As a result of our investigation into the process variables that led to this wholly unexpected discovery, we have developed a new process for producing rayon filaments and staple fibers that are characterized by an extremely high number of crimps or undulations per inch as well as by high conditioned and wet tenacity and high wet modulus.

Summary of the Invention The process for making high crimp, high tenacity rayon fiber of our invention comprises spinning a modified viscose spinning solution of the type described in the aforementioned US. Pat. No. 3,494,996 into a coagulating-type spin bath at a temperature of 18 to 40 C. to obtain coagulated, incompletely regenerated viscose filaments. The coagulated viscose filaments are withdrawn from the spin bath, and while the filaments are still substantially soluble in dilute alkali solution, the filaments are stretched from about 150 to 180 percent in length and at the same time are treated with a hot dilute acid bath to partially regenerate the filaments. The tension of the filaments is then relaxed about 20 to 60 percent while the filaments are less than 50 percent regenerated, and the relaxed, partially regenerated filaments are treated with an alkaline solution having a pH of from about 7.5 to 10. The alkaline solution is advantageously a dilute aqueous solution of sodium carbonate, sodium bicarbonate, or sodium hydroxide, and the filaments are treated with this solution for a period of time and at a temperature ranging from about 2 seconds at 100 C. to about 120 seconds at about 20 C. On completion of the alkaline treatment, the regeneration of the filaments is completed by conventional procedures without additional stretching. The completely regenerated filaments are then desulfurized and washed in the usual manner. Alternatively, on completion of the acid regeneration treatment, the

filaments can be cut into staple fibers and these staple fibers desulfurized and finished as described. The resulting filaments or staple fibers have between 30 and 150, and normally more than 40, crimps per inch in the relaxed condition, a conditioned tenacity of greater than 3 gpd, a wet tenacity of greater than 2 gpd, and a wet modulus of greater than 0.4 gpd.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION The preparation of a modified viscoe spinning solution suitable for use in the process of our invention has been described in US. Pat. No. 2,942,931 that issued June 28, 1960. Such spinning solutions are formed from cellulose xanthate having a relatively uniform chain length with a degree of polymerization (DP) of from about 450 to 800 and a suitably balanced ratio of cellulose and sodium hydroxide within the range of about 4 to 9 percent in the viscose. In the patented process, purified chemical cellulose such as bleached sulfite and prehydrolyzed kraft wood pulps as well as cotton linters having relatively high uniform DP are converted into alkali cellulose and xanthated with 32 to 44 percent carbon bisulfite at ambient temperatures in the usual manner. The viscose is modified with a mixed modifier comprising from 1.0 to 3.0 percent dimethylamine (DMA) and from 0.5 to 2.5 percent polyethylene glycol (PEG) on the weight of the cellulose which may be added at any stage prior to spinning but preferably during mixing. The salt (NaCl) index of the spinning solution should be between about 7 and 12 (preferably between 9 and 11) and the gamma number between about 40 and (preferably between 50 and 80) when spun with ripening selected to attain this level. The salt index and gamma number, of course, depend upon the amount of carbon bisulfide used in xanthation, the temperature of the reaction and the amount of ripening used.

The viscosity of the spinning solution is not particularly critical and can range between about 20 and ball fall seconds (bfs). This is an advantageous viscosity level since most processes for spinning high tenacity filaments require high viscosities (up to about 400 bfs) to produce satisfactory high tenacity fiber. High viscosity makes accurate denier control difficult and interferes with mixing, deaeration, filtration, pumping and spinning processes.

Referring now to FIGS. 1 and 2 of the drawing, in the process of the invention the modified viscose solution is spun at 18 to about 40 C. (preferably 20 to 25 C.) through a spinnerette 10 into a coagulating-type spin bath. 11 advantageously containing 0.2 to 2.0 percent by weight formaldehyde, 1 to 6 percent by weight zinc sulfate, 3 to 9 percent by weight sulfuric acid and from 7 to 18 percent by weight sodium sulfate. The spin bath 1 1 may also contain from 0.01 to 0.1 percent by weight of a surface active agent or lubricant such as lauryl pyridinium chloride (1pc) and the like. Travel of the filaments 12 through this bath should be limited to that required to develop sufficient strength for stretching in order to avoid any unnecesary regeneration. While the distance from spinnerette 10 to emergence of the filaments 12 from the bath 11 can vary from about 4 to 48 inches or more, depending upon spinning speed, spin bath temperature, composition of the viscose, etc., less than 25 inches will usually be sufficient. We have found, for example, that l2 to 15 inches immersion is optimum for spinning speeds of 25 to 30 meters per minute and wind-up.

Almost immediately after leaving the coagulating spin bath 11 the filaments 12 as a group or tow and while they are still completely soluble in dilute alkali, are stretched from about 150 to 280 percent. To effect this stretch, the tow withdrawn from the bath is passed around a driven godet 13 and then several times around one or more godets 14 driven at a sufficiently greater speed to provide the desired continuous stretching. At the same time, the stretched, coagulated filaments (or tow) 12 are partially regenerated by treating the filaments with a hot dilute acid bath, preferably by passing the filaments through an aqueous solution 15 containing about 0.5 to 5, and preferably about 3, percent by weight H SO and maintained at a temperature of from about 60 to 100C., and preferably about 80C.

Immediately following the stretching and hot acid treatment, the incompletely regenerated filaments are relaxed and, while relaxed and less than 50 percent regenerated, are treated with a dilute alkaline solution at a pH of from about 7.5 to 10. Thus, as shown in FIG. 2, the filaments or tow 12 are advantageously washed at godet or reel 14 by means of the spray heads (or equivalent device) 16. The washed filaments are treated with a dilute alkaline solution at reel 17 by means of the spray heads 18, the filaments being less than 50 percent regenerated (that is, at least 50 percent of the coagulated material being soluble in dilute caustic soda) and the alkaline solution having a pH of from about 7.5 and 10. The treated filaments 12 are allowed to relax from about 20 to 60 percent between the reels l7 and 19 by reducing the speed of the reel 19 relative to the speed of reels l4 and 17. As a result of this alkaline treatment of the relaxed, partially regenerated filaments, a highly crimped filament or staple fiber product is obtained.

As noted, the pH of the alkaline solution is between about 7.5 and 10, and it advantageously comprises a dilute aqueous solution of sodium carbonate or sodium bicarbonate or a very weak solution of sodium hydroxide. The relationship between the time and temperature of the alkaline treatment is important, the usual range being from about 2 seconds at about lC. to about 120 seconds at ambient temperature (about 20 to 30C.). The frequency and amplitude of the crimp produced can be controlled by controlling the amount of stretch, the pH and the temperature of the alkaline treatment solution, and the amount of relaxation allowed. To obtain high crimp, high tenacity fiber having from 30 to 150 crimps per inch and a conditioned tenacity of from 3 to gpd, the essential requirement is that the aforementioned process variables be within the limits herein set forth.

Following the alkaline treatment step of the process, the highly crimped filaments are completely regenerated, desulfurized, washed, finished and dried by conventional techniques. Thus, referring again to FIG. 2,

the highly crimped filaments are treated at reel 19 with an acid regenerating solution (for example, a hot dilute solution of sulfuric acid) and then with wash water by means of the spray heads 20, are treated at reel 21 with a desulfurizing solution (for example, a hot dilute solution of sodiumsulfide) and then with wash water by means of the spray heads 22, and are treated at reel 23 with an acid solution (for example, cool dilute sulphuric acid) and then with wash water by means of the spray heads 24. The regenerated, desulfurized filaments are then treated with a finishing solution 25, dried at drying reel 26 and collected on bobbin 27.

Alternatively, the crimped filaments, after regeneration, can be cut into staple fibers and these staple fibers can then be desulfurized, washed, finsihed and dried in the usual manner. Thus, again referring to FIG. 2, the crimped, unfinished filaments are treated at reel 19 with a hot acid regenerating solution, and are washed at reels 21 and 23 with hot water. The washed, regenerated filaments are then cut into staple fibers about an inch and a half in length, and these staple fibers are desulfurized, neutralized, washed and finished in an entirely conventional manner.

The highly crimped, high strength rayon filaments and staple fibers produced by our new process have more than 30 crimps per inch, and ordinarily have from 40 to 150 crimps per inch. The conditioned tenacity of the fibers is greater than 3 gpd, and normally is between 3 and 5 gpd. The wet tenacity of the fibers is greater than 2 gpd, and the wet modulus (wet tenacity at 5 percent elongation) is greater than 0.4 gpd. Other physical characteristics include a water retention of about 80 to I50 percent on the crimped fiber (as compared to a water retention of about percent of the uncrimped fiber produced by the process of copending application Ser. No. 473,321 and the cross-section of the fiber has a multi-protuberance profile.

The following examples are illustrative but not limitative of the practice of our invention.

EXAMPLE I A modified viscose spinning solution containing 6 percent cellulose and 6 percent NaOl-l was produced from alkali-treated chemical cellulose using 38 percent CS The viscose contained 2.3 percent dimethylamine and 1.7 percent polyethylene glycol (both based on weight of cellulose). Xanthate sulfur was 1.5 percent, viscosity was 40 ball fall seconds, and NaCl index was 12.

Referring now to FIG. 2, the well-deaerated viscose was extruded through a spinnerette 10 with 3,000 holes of 0.0025-inch diameter each, into a spin bath 11 containing 6.5 percent H 10 percent Na SO.,, 2.5 percent ZnSO, at a temperature of 25C. The coagulated tow 12 was wrapped around a godet l3 and led through a hot secondary acid bath 15 to a wash reel 14 on which it was wrapped several times to prevent slippage.

Before passing through the hot secondary acid bath 15, the coagulated viscose fiber was practically completely soluble in dilute alkali such as 1 percent NaOH. The secondary acid bath contained about 3.5 percent H 80, and residues of salts carried over from the primary bath 11. It was maintained at C, spinning speed was about 25 meters/minute and stretch between the first godet 13 and first wash reel 14 was 260 percent. Y

A sample of tow, cut and removed from the first reel 14 was still about 70 percent soluble in dilute caustic soda, showing incomplete regeneration at this point. A water solution of 0.5 percent sodium bicarbonate at 50C. was applied to the second wash reel 17 and the tow allowed to relax between wash reels 17 and 19 about 30 percent. This was accomplished by reducing the speed of wash reel 19 relative to that of 17.

Hot dilute acid was applied to wash reel 19, and hot water was applied to wash reel 21 and 23.

The tow was collected wet, cut into staple fiber lengths of about 1 9/ 16-inch, desulfurized, neutralized, washed and finished in the usual manner with a staple fiber finish. After drying and conditioning, single filament tests were run under standard procedures.

Results of these tests are shown in Table 1 below, together with comparable data for control fibers produced without the relaxed, bicarbonate treatment in accordance with the process of application Ser. No. 473,321 and the properties of commercially produced super-crimp rayon fibers.

A comparison of the properties of the two crimped fibers set forth in columns B and C of Table 1 shows the superiority of the tenacity, modulus and number of crimps of the rayon fibers of the invention over ordinary, commercial crimped rayon fibers.

TABLE 1 B Uncrimped Crimped Fiber Commercial Fiber of Ser. No. 473,321 of the lnven- Supertion Crimped Rayon Denier 1.5 1.8 1.5

Tenacity, g./d.

Cond. 6.0 4.0 1.8 2.7 Wet 4.8 2.7 1.0 1.6

Elongation, 7c 1 Cond. 9.0 10.8 18 30 Wet 10.0 13.6 24 40 Wet Tenacity at 5% E1. g /d (Wet 1.8 0.8 0.2 Modulus) Crimps/inch 6 65 12 25 Water 65 120 80 Retention,

EXAMPLE 2 The procedure of Example 1 was followed except that a very dilute solution of NaOH with just enough NaOH to bring water to a pH of was applied to wash reel 17 (instead of the 0.5 percent sodium bicarbonate solution) and a relaxation of about 50 percent wash reels 17 and 19 was obtained. 1

In this case the following fiber properties were obtained Denier, 2.3; Tenacity: Cond., 3.3 gpd.; wet 2.4 gpd; Elongation: Cond., 15.0 percent; wet, 17.8 percent; Wet tenacity at 5 percent elongation, 0.5 gpd; Crimps/inch, 100. The finished fiber was extremely bulky and had a soft, wool-like hand.

EXAMPLE 3 Strong, highly crimped fibers with conditioned tenacities of from 3.0 to 5.0 gpd, wet tenacities of from 2.0 to 3.8 gpd and wet moduli of from 0.5 to 1.0 gpd were obtained using the procedure of Example 2. except for application of the following solutions to wash reel 17,

a. 0.2 percent Na CO at 25 C.,

b. 0.2 percent Na CO at 50 C.,

c. 0.005 percent NaOH at 50 C., and

d. 1.0 percent Na1-1CO at 25 C.

The use of a 1.0 percent NaOH solution at 25C., on the other hand, resulted in a partially dissolved, gelatinuous tow demonstrating the need for maintaining the pH within the indicated ranging during this step of the process.

EXAMPLE 4 The procedure of Example 1 was followed except that after treatment of the tow with the 0.5 percent sodium bicarbonate solution on wash reel 17, the following succession of treatments was applied:

a. Hot, dilute H SO (l percent) was applied to the first half of wash reel 19, and hot water (C.) to the second half.

b. Desulfurizing solution (1 percent Na S) at 60C. was applied to the first half of wash reel 21, and hot water (85C) to the second half.

c. Dilute (1 percent) H 50 was applied to the first quarter of wash reel 23 and hot water to the balance.

d. The tow was passed through a finished solution 25, dried on the drying reel 26 and collected on bobbins 27.

This experiment demonstrated the practicality of producing crimped or latent-crimped continuous filaments by the process of this invention.

Samples of the dried filaments did not appear to have as many crimps as those of Example 1 (finished in the relaxed state). However, when placed additional crimp developed by relaxation of the filaments which had been dried under very slight tension. Thephysical properties were similar to those of the fibers in Example 1.

We claim:

1. High crimp, high tenacity rayon fibers having more than 30 crimps per inch (relaxed), a conditioned tenacity greater than 3 grams per denier (gpd), a wet tenacity greater than 2 gpd, and a wet tenacity at 5 percent elongation (wet modulus) greater than 0.4 gpd.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,793,136 Dated February 19, 1974 Inventor(s) George Daul et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The term of this patent subsequent to Jan. 4, 1989, has been disclaimed.

- 7'?- .-1; ;ne:? and sealed thls 15th day of aerrl 1.73.

F ORM PO-OSO (10-69) USCOMM-DC 603764 69 15 GOVERNMENT PRINT NG OFF CE 9 9 

